This invention relates generally to computer controlled systems and particularly to a system for converting the frequency of a pulse train to a binary number and providing said number to the computer of such a system.
An example of a system which requires the conversion of the frequency pulse train to a binary number is a computer controlled lighthouse which is used to expose the black matrix material on the inside surface of a color kinescope baseplate panel. In applying the black matrix to such a panel, a photosensitive black slurry material is applied to the inside of the faceplate and a shadow mask is inserted into the panel. Intense light from the lighthouse lamp passes through the apertures in the shadow mask to expose portions of the slurry. The shadow mask is subsequently removed from the panel and the unexposed material is washed away leaving a series of black lines which compose the black matrix. Uniformity of product requires that the exposure of the matrix material remain constant even though the light output of the lighthouse lamp may vary because of variations in the voltage applied to the lamp or because of degregation of the lamp. Thus, as the intensity of the lamp decreases, the length of time that the slurry is exposed to the light must be increased to maintain a constant light intensity/time multiple. Conversely, if the intensity of the lamp increases, the exposure time must be proportionately decreased to maintain a constant intensity/time multiple. One method of maintaining a constant intensity/time multiple is to monitor the intensity of the lamp and provide a pulse train the frequency of which varies along with the lamp intensity. The pulse train frequency changes are detected and used as a measure of the exposure time adjustment needed to maintain a constant intensity/time multiple.
An example of a system which operates in this manner is described in Patent Application Ser. No. 267,750 filed May 28, 1981 by William R. Kelly and Ernesto J. Alvero and entitled "System and method For Controlling The Exposure Of Color Picture Tube Phosphor Screens", now U.S. Pat. No. 4,436,394. In the system described in this patent application, the changes in the frequency of a pulse train occasioned by variations in lamp intensity are processed within the lighthouse control system and used to adjust the exposure time. This results in some disadvantage because the frequency must be converted to a binary number to which the computer can respond. Making the conversion internally of the control system consumes control system time and calculating capability and thus preferably should be made external of the control system.
The instant invention overcomes this disadvantage by the provision of a system for converting a frequency to a binary number representative of the frequency and supplying the binary number to the computer of a computer controlled system.